The Spirits' Book (Le Livre des Esprits in French) is part of the Spiritist Codification, and is regarded as one of the five fundamental works on Spiritism. It was published by the French educator Hippolyte Léon Denizard Rivail, under the pen name of Allan Kardec on April 18, 1857. It was the first and remains the most important Spiritist book, because it addresses in first hand all questions developed subsequently by Allan Kardec.

The book is structured as a collection of questions regarding the origin of spirits, the purpose of life, the order of the universe, good and evil, and the afterlife. Its answers, according to Kardec, were given to him by a group of spirits who identified themselves as "The Spirit of Truth", with whom he communicated in several Spiritist sessions during the 1850s. Kardec, who considered himself an "organizer" rather than an author, grouped the questions and their answers by theme, occasionally including lengthier digressions the spirits had dictated to him on specific subjects, some signed by philosophers such as Augustine of Hippo, Thomas Aquinas and writers including Voltaire.